Add API and signaling to accept incoming channels at 0conf

Author: TheBlueMatt

lightning/src/ln/channel.rs

@@ -1265,7 +1265,7 @@ impl<Signer: Sign> Channel<Signer> {
 			counterparty_htlc_minimum_msat: msg.htlc_minimum_msat,
 			holder_htlc_minimum_msat: if config.own_channel_config.our_htlc_minimum_msat == 0 { 1 } else { config.own_channel_config.our_htlc_minimum_msat },
 			counterparty_max_accepted_htlcs: msg.max_accepted_htlcs,
-			minimum_depth: Some(config.own_channel_config.minimum_depth),
+			minimum_depth: Some(cmp::max(config.own_channel_config.minimum_depth, 1)),
 
 			counterparty_forwarding_info: None,
 
@@ -4797,6 +4797,12 @@ impl<Signer: Sign> Channel<Signer> {
 		self.inbound_awaiting_accept
 	}
 
+	/// Sets this channel to accepting 0conf, must be done before `get_accept_channel`
+	pub fn set_0conf(&mut self) {
+		assert!(self.inbound_awaiting_accept);
+		self.minimum_depth = Some(0);
+	}
+
 	/// Marks an inbound channel as accepted and generates a [`msgs::AcceptChannel`] message which
 	/// should be sent back to the counterparty node.
 	///

lightning/src/ln/channelmanager.rs

@@ -4352,18 +4352,43 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 		}
 	}
 
-	/// Called to accept a request to open a channel after [`Event::OpenChannelRequest`] has been
-	/// triggered.
+	/// Accepts a request to open a channel after a [`Event::OpenChannelRequest`].
 	///
 	/// The `temporary_channel_id` parameter indicates which inbound channel should be accepted.
 	///
-	/// For inbound channels, the `user_channel_id` parameter will be provided back in
+	/// The `user_channel_id` parameter will be provided back in
 	/// [`Event::ChannelClosed::user_channel_id`] to allow tracking of which events correspond
 	/// with which `accept_inbound_channel` call.
 	///
 	/// [`Event::OpenChannelRequest`]: events::Event::OpenChannelRequest
 	/// [`Event::ChannelClosed::user_channel_id`]: events::Event::ChannelClosed::user_channel_id
 	pub fn accept_inbound_channel(&self, temporary_channel_id: &[u8; 32], user_channel_id: u64) -> Result<(), APIError> {
+		self.do_accept_inbound_channel(temporary_channel_id, false, user_channel_id)
+	}
+
+	/// Accepts a request to open a channel after a [`events::Event::OpenChannelRequest`], treating
+	/// it as confirmed immediately.
+	///
+	/// The `user_channel_id` parameter will be provided back in
+	/// [`Event::ChannelClosed::user_channel_id`] to allow tracking of which events correspond
+	/// with which `accept_inbound_channel` call.
+	///
+	/// Unlike [`ChannelManager::accept_inbound_channel`], this method accepts the incoming channel
+	/// and (if the counterparty agrees), enables forwarding of payments immediately.
+	///
+	/// This fully trusts that the counterparty has honestly and correctly constructed the funding
+	/// transaction and blindly assumes that it will eventually confirm.
+	///
+	/// If it does not confirm before we decide to close the channel, or if the funding transaction
+	/// does not pay to the correct script the correct amount, *you will lose funds*.
+	///
+	/// [`Event::OpenChannelRequest`]: events::Event::OpenChannelRequest
+	/// [`Event::ChannelClosed::user_channel_id`]: events::Event::ChannelClosed::user_channel_id
+	pub fn accept_inbound_channel_from_trusted_peer_0conf(&self, temporary_channel_id: &[u8; 32], user_channel_id: u64) -> Result<(), APIError> {
+		self.do_accept_inbound_channel(temporary_channel_id, true, user_channel_id)
+	}
+
+	fn do_accept_inbound_channel(&self, temporary_channel_id: &[u8; 32], accept_0conf: bool, user_channel_id: u64) -> Result<(), APIError> {
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(&self.total_consistency_lock, &self.persistence_notifier);
 
 		let mut channel_state_lock = self.channel_state.lock().unwrap();
@@ -4373,6 +4398,7 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 				if !channel.get().inbound_is_awaiting_accept() {
 					return Err(APIError::APIMisuseError { err: "The channel isn't currently awaiting to be accepted.".to_owned() });
 				}
+				if accept_0conf { channel.get_mut().set_0conf(); }
 				channel_state.pending_msg_events.push(events::MessageSendEvent::SendAcceptChannel {
 					node_id: channel.get().get_counterparty_node_id(),
 					msg: channel.get_mut().accept_inbound_channel(user_channel_id),

lightning/src/ln/priv_short_conf_tests.rs

@@ -550,15 +550,27 @@ fn test_simple_0_conf_channel() {
 
 	let chanmon_cfgs = create_chanmon_cfgs(2);
 	let node_cfgs = create_node_cfgs(2, &chanmon_cfgs);
-	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, None]);
+	let mut chan_config = test_default_channel_config();
+	chan_config.manually_accept_inbound_channels = true;
+
+	let node_chanmgrs = create_node_chanmgrs(2, &node_cfgs, &[None, Some(chan_config)]);
 	let nodes = create_network(2, &node_cfgs, &node_chanmgrs);
 
 	nodes[0].node.create_channel(nodes[1].node.get_our_node_id(), 100000, 10001, 42, None).unwrap();
 	let open_channel = get_event_msg!(nodes[0], MessageSendEvent::SendOpenChannel, nodes[1].node.get_our_node_id());
 
 	nodes[1].node.handle_open_channel(&nodes[0].node.get_our_node_id(), InitFeatures::known(), &open_channel);
+	let events = nodes[1].node.get_and_clear_pending_events();
+	assert_eq!(events.len(), 1);
+	match events[0] {
+		Event::OpenChannelRequest { temporary_channel_id, .. } => {
+			nodes[1].node.accept_inbound_channel_from_trusted_peer_0conf(&temporary_channel_id, 0).unwrap();
+		},
+		_ => panic!("Unexpected event"),
+	};
+
 	let mut accept_channel = get_event_msg!(nodes[1], MessageSendEvent::SendAcceptChannel, nodes[0].node.get_our_node_id());
-	accept_channel.minimum_depth = 0;
+	assert_eq!(accept_channel.minimum_depth, 0);
 	nodes[0].node.handle_accept_channel(&nodes[1].node.get_our_node_id(), InitFeatures::known(), &accept_channel);
 
 	let (temporary_channel_id, tx, _) = create_funding_transaction(&nodes[0], 100000, 42);

lightning/src/util/config.rs

@@ -21,7 +21,14 @@ pub struct ChannelHandshakeConfig {
 	/// Applied only for inbound channels (see ChannelHandshakeLimits::max_minimum_depth for the
 	/// equivalent limit applied to outbound channels).
 	///
+	/// A lower-bound of 1 is applied, requiring all channels to have a confirmed commitment
+	/// transaction before operation. If you wish to accept channels with zero confirmations, see
+	/// [`UserConfig::manually_accept_inbound_channels`] and
+	/// [`ChannelManager::accept_inbound_channel`].
+	///
 	/// Default value: 6.
+	///
+	/// [`ChannelManager::accept_inbound_channel`]: crate::ln::channelmanager::ChannelManager::accept_inbound_channel
 	pub minimum_depth: u32,
 	/// Set to the number of blocks we require our counterparty to wait to claim their money (ie
 	/// the number of blocks we have to punish our counterparty if they broadcast a revoked